The treatment, such as epitaxy of a silicon-based substrate, requires that the substrate has a clean surface in order to obtain an epitaxy of good quality. It seems therefore necessary to remove the native oxide, the carbon and any other impurities present on the surface of the substrate.
In the aforesaid preferred application, namely epitaxy on silicon, the prior art has proposed the use, as method for cleaning the surface of a substrate, of thermal etchings conducted at relatively high temperatures, around 800.degree. to 900.degree. C., and resulting from the conversion of silicon oxide into volatile species.
These cleaning methods, which are performed at relatively high temperatures, are not suitable for the production of microelectronoic components of ULSI (Ultra Large Scale Integration) type. Indeed, it is impossible when using a very high heating power, to preserve the sharp doping profiles of the substrates. Also, the use of high temperatures is incompatible with the operation of new microelectronic structures, such as heterostructures or heteroepitaxies.
In an attempt to overcome these drawbacks, the prior art has proposed to use an ion bombardment in order to effect such cleanings at lower temperatures. To this effect, the document by B. ANTHONY et al., J. Vac. Sci. Technol., B7, page 621, 1989, has recommended the use of hydrogen plasmas to ensure said etching function. But it has been found that such a plasma does not make it possible to remove easily the native oxide present on the surface of the silicon. Moreover, a hydrogen plasma etches the silicon much quicker than silica and any roughness on the surface of the silica will be transferred and accentuated in the silicon.
Furthermore, the documents by T. J. DONAHUE et al., J. Appl. Phys. 57, page 2757, 1985 and by COMFORT et al., J. Appl. Phys. 62, page 3388, 1987, have also proposed the use of argon plasmas which are known to act according to the spraying mechanism. The use of argon plasmas implies using strong energy-producing ions which cause defects in the silicon, as well as an implantation of argon in the substrate. Consequently, argon plasmas are used at a sufficiently high temperature and are generally followed by annealing at relatively high temperature, around 800.degree. C., to eliminate all the defects created by said technique.
Finally, the document by TRI-RUNG YEW et al., J. Appl. Phys. 68, page 4681, 1990 has recommended to subject the substrate to a plasma of argon mixed with hydrogen, in temperature conditions of about 700.degree. C.
The analysis made of the prior art has therefore revealed that there is a need to find a method for low temperature cleaning of the surface of a substrate, to be implemented before another treatment such as epitaxy or deposition.